The coagulation of milk, which is effected under all sorts of conditions depending on the nature of the cheeses which are to be prepared, produces not only a casein coagulum but also milk serum, the characteristics of the composition of which vary as a function of numerous parameters such as the source of the milk and the treatment which it has undergone.
Generally, the coagulum is separated from the milk serum, and this serum is then processed by subjecting it to various treatments, including ultrafiltration, to prepare useful milk serum proteins, more particularly as ingredients for dietetic foods.
The residue should contain as few lipids as possible, particularly if protein-enriched foods are to be prepared. During ultrafiltration, lipoproteins accumulate and form part of what is referred to as a dynamic membrane which lowers the permeation flow rates and makes it more difficult to clean the apparatus afterwards. In some cases there is also a detrimental increase in viscosity and a reduction in foaming power and stability.
All the solutions proposed up till now for reducing the lipid content of the milk serum, such as microfiltration, demineralisation followed by heat treatment and heating to elevated temperature, are laborious and not very effective.